DESCRIPTION: The natural acoustic environment of a listener is typically composed of multiple sound sources, each of which is spectrally complex and usually fluctuating in intensity. The ability of a listener to sensibly sift apart the multiple sound sources superimposed in the impinging sound wave constitutes the broad topic of perceptual organization. One of the main goals of this Project is to understand the role of amplitude modulation in the perceptual organization of spectrally-complex sound. This necessitates an understanding of the underlying processes involved in across-frequency temporal analysis. The other main Project goal concerns the effects of cochlear hearing loss on perceptual organization. Successful processing of a complex sound is affected by the fidelity with which the sound is encoded in the peripheral auditory system. Reductions in the information content of the encoded sound due to cochlear dysfunction must challenge more central stages of auditory processing. The proposed Project is broken down into three related Study Areas. The first Study Area examines across-frequency temporal processing in both normal-hearing and cochlear-impaired listeners. The second Study Area develops a general model of modulation processing where a tight linkage is maintained between the fluctuation pattern itself and the specific frequencies on which the fluctuation pattern is imposed. The third Study Area investigates the perceptual organization of multiple simultaneous modulation patterns. The results of this Project will provide a better understanding of the processes underlying perceptual organization in normal-hearing listeners and an objective appreciation of the difficulties experienced by listeners with cochlear hearing loss in competitive listening situations.